4 Answers
4

The specific requirements for a 2GB stick is so you can install a persistent file to the USB disk so that if you require a certain package on the LiveUSB, you will have more than enough space.

The persistent filesystem for the disk requires at least (from the experiences I've had) 500MB to efficiently operate (see the below section titled "EDIT" for details on this number). That is the reason for the 2GB USB stick requirement.

EDIT
The source for this information was testing I've done in the past. I have 1GB, 2GB, and 8GB sticks here, and making the bootable USB disc through the USB Startup Creator tool in 10.04, the persistent filesystem does not effectively operate at the 1GB level, works fairly well at the 2GB level, and works great at the 8GB level.

I think they have the 2gig thing for if you are not only installing Ubuntu on a computer but to use it on other computers just temporarily. The 2gig could be a minimum recommendation for saving files to the flash drive.